The present invention relates to high frequency chest wall oscillator (referred to hereafter as HFCWO) devices.
In a variety of diseases such as cystic fibrosis, emphysema, asthma, and chronic bronchitis, the mucus that collects in the airways is difficult to remove by coughing. This may be due to the viscosity or quantity of the mucus or because the patient does not have the strength or lung capacity to produce an adequate cough. Prior art HFCWO devices have been developed that are commercially available standards of care for airway mucus clearance. They promote airway mucus clearance by generating rapidly oscillating externally powered cough like air flows and pressures in the airways of a patient. U.S. Pat. Nos. 7,762,967, 7,115,104, 6,254,556 and 6,036,662 disclose the designs of some popular devices. These are typically prescribed to be used once or several times per day, in sessions of up to about 30 minutes each.
Popular prior art devices are composed of an air pulse generator connected by pneumatic tubing to a vest like garment with an air bladder worn in contact with and surrounding a person's chest. Air pulses cyclically oscillate to alternately pressurize and depressurize the bladder to apply cyclic pressures to the person's chest. Cycle rates can typically be selected from between about 5 to 25 cycles per second. Many of these devices use an air pulse generator that cycles the bladder pressure between about 0 to 1 PSI. Power consumed by some of these devices at the high frequency settings has been measured to be over 200 watts. We have found that, at cycle rates above about 12 cycles per second, an increasing majority of this power is wasted due to inertial effects of the pressure pulses rapidly reversing directions through the tubes connecting the pressure generator and the vest as well as turbulent flow of the transferred volumes of air throughout the system.
A portable solution was attempted as disclosed in U.S. Pat. No. 6,736,785. This invention included a band wrapped around the chest of a person. The circumference of the band was oscillated by mechanical means to apply oscillating force on the person's chest. Several means for allowing chest movement during inspiration and expiration were also disclosed. This design eliminated the energy losses associated with the high air flows within and between the system components of the popular pneumatic systems which demonstrated significant power reductions. Also the mechanical oscillator was much smaller than the pneumatic oscillators. However, this design was not developed into a fully practical device. The chest band concentrated the pressure on the chest to a much smaller area than that of pneumatic vests disclosed in prior art. Because of this, for an effective amount of energy transfer to the person's chest, it was found that an intolerable level of discomfort resulted which would greatly reduce compliance to a prescribed usage routine. This was most severe at higher oscillation frequencies. With the disclosed chest band design the mechanism that oscillated the band produced chest pressure variations that were constant in amplitude over the range of oscillation frequencies. With this, as the frequency increased, the energy transfer to the chest increased proportionately. Allowing a 4:1 ratio of high to low frequency, the energy transfer became excessive and intolerable at high frequencies. Many of the other prior art devices use a constant displacement type pump or reciprocating diaphragms to generate the pressure pulses so, in theory, these would be expected to present the same problem of excessive energy to the persons chest at high frequencies. Measurements show that they actually do, but to a much lesser extent than theory would predict. This is because the substantial air flow related power losses of the pneumatic systems increase rapidly with increasing frequency and tend to attenuate the pulses delivered to the vest and person's chest at those higher frequencies. U.S. Pat. No. 7,785,280 discloses a means of varying the stroke length of a pneumatic type pressure oscillator that could correct this and provide other benefits. To solve this problem in a portable system something similar to the variable stroke mechanism of U.S. Pat. No. 7,785,280 could, in concept, be included but the added complexity and size of the various linkages and control may be poorly suited to a compact wearable device.
Reliable and failsafe operation of all these devices is important. To be offered commercially for medical treatment of people, an FDA approval based on extensive safety analysis is required. This includes consideration of potential device malfunction and misuse. The potential to transfer injurious forces to the chest of the person due to improper use is possible with some prior art designs, as is the possibility of a device malfunction that prohibits the benefits of using such devices.
Efficacy of new devices is also a requirement for FDA approval. Experience with the application of these types of devices has proven that their efficacy is maximized when they have simple user controls, generate proven effective chest wall oscillation wave shapes, amplitudes and frequencies, and encourage compliance to a prescribed usage routine through optimized comfort, ease of use and vanity issues. The present invention provides improvements that encourage compliance to prescribed usage enhancing the long term efficacy of the device. It also provides improvements in the generation and control of the chest wall oscillation waveform to enhance the efficiency of each airway clearance session.
This disclosure provides a system including an air pulse generator, a power source and a vest that are uniquely small and efficient enough to be integrated into a wearable and transportable portable device for use on an ambulatory patient. Treatment sessions with this would be less intrusive allowing a person to stand and move about at will during the sessions rather than being confined to a support, such as a bed. Also, evidence shows that HFCWO is more effective when the person is standing. It is projected that exercise during treatment sessions could also increase the efficacy of HFCWO.
When the pressure generator and power source are integrated with the vest and worn on the person, additional safety features are needed in the design. Risks not present with a sedentary device arise when all these components are strapped to the person. The disclosed invention is a unique and effective solution that is portable, wearable, comfortable, safe and easy to use having the ability to vary the amplitude of the oscillating air pulses as needed to optimize efficacy as oscillation frequency, patient size and disease conditions vary.